# Can we simulate Earth's gravity in space?

Earth gravity is 9.8 $ms^{-2}$

Gravity on ISS(international space station) is 8.2 $ms^{-2}$ approx.

As per this https://physics.stackexchange.com/questions/29929/gravity-on-the-international-space-station ISS never hit the ground because of it's vertical velocity.(free fall)

My question:

Can we create artificial gravity on ISS by using centrifugal force? [Have anyone watched "The martian"? they have used this technique]

• Yes, it does exist. en.wikipedia.org/wiki/Artificial_gravity
– Jed
Nov 29 '15 at 1:20
• in The Martian, Hermes span to generate martian gravity, 2/5 of the earths gravity. Nov 29 '15 at 9:56

Simulating gravity in space basically means simulating weight, which requires acceleration. So basically, the question is, how do we create acceleration in space.

The easiest method for simulating gravity in space is by spinning the space station. In this case, the reaction force to centripetal force substitutes the force of gravity, which pushes the inner contents to be pushed against the outer edge, giving a sensation of weight. This method is theoretically sound and can be used to simulate gravity.

The problem with doing this in ISS boils down to two things- size and shape.

The best shape for a space station having a simulated gravity is something like a doughnut spinning about its axis, so that the occupants are pushed against the outer wall. The shape of ISS is nowhere near this.

If one excludes the solar panels and the truss structure, the ISS is around 45m along the axis of the habitable modules, if we spin along the axis of the truss structure, this gives a radial distance of ~22.5m.

For simulating earth's gravity in ISS, we will require,

$$\omega^{2} r = g$$

$$\omega = \sqrt{\frac{g}{r}}$$

For g = 9.8 $ms^{-2}$,

$$\omega = \sqrt{\frac{9.8}{22.5}} = 0.66 rad/sec = 6.3 rpm$$

The problem is that at this rotational speed, the head and foot of the astronomer will have different linear velocities. The head of a 1.5m tall astronaut will be moving at 13.86 $ms^{-1}$, while the foot will be moving at 14.85 $ms^{-1}$, never mind they are standing at the bottom of a barrel. This will lead to Coriolis effect, which will be uncomfortable.

So, while earth's gravity cannot be simulated in ISS due to various constraints, we can settle for reduced gravity (with reduced, ~2 rpm) in an ISS sized spacecraft.

• An alternative to the doughnut, and a way to reduce the Coriolis effect could be a long tether and a large weight, perhaps a spinning but very solid asteroid with a 600 meter tether to a ship, doing 1 RPM, but that wouldn't be precisely easy either, and they'd be in trouble if the tether snapped so the ship would need sufficient boosters just in case. This isn't precisely what I mean, but it's the idea. The videos are worth a look. science20.com/robert_inventor/… Nov 29 '15 at 14:08